Question

10. (a) The persistent organic pollutants (POPs) that transport via atmosphere into the Arctic have their unique chemical signature. Explain this statement by comparing their chemical properties with POPs that stay near the source region and appropriate examples. (b) Describe the significance of the global distillation model in understanding the long-distance transport of POPs to the arctic. (c) What are the long-term ecological and human ramifications of POPs contamination in the arctic.

Answer 1

Persistent organic pollutants (POPs), sometimes known as "forever chemicals" are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of their persistence, POPs bioaccumulate with potential adverse impacts on human health and the environment. The effect of POPs on human and environmental health was discussed, with the intention to eliminate or severely restrict their production, by the international community at the Stockholm Convention on Persistent Organic Pollutants in 2001.

Many POPs are currently or were in the past used as pesticides, solvents, pharmaceuticals, and industrial chemicals. Although some POPs arise naturally, for example, volcanoes and various biosynthetic pathways, most are man-made via total synthesis.

POPs typically are halogenated organic compounds (see lists below) and as such exhibit high lipid solubility. For this reason, they bioaccumulate in fatty tissues. Halogenated compounds also exhibit great stability reflecting the nonreactivity of C-Cl bonds toward hydrolysis and photolytic degradation. The stability and lipophilicity of organic compounds often correlate with their halogen content, thus polyhalogenated organic compounds are of particular concern. They exert their negative effects on the environment through two processes, long-range transport, which allows them to travel far from their source, and bioaccumulation, which reconcentrates these chemical compounds to potentially dangerous levels. Compounds that makeup POPs are also classed as PBTs (Persistent, Bioaccumulative, and Toxic) or TOMPs (Toxic Organic Micro Pollutants).

Global distillation or the grasshopper effect is the geochemical process by which certain chemicals, most notably persistent organic pollutants (POPs), are transported from warmer to colder regions of the Earth, particularly the poles and mountain tops. Global distillation explains why relatively high concentrations of POPs have been found in the Arctic environment and in the bodies of animals and people who live there, even though most of the chemicals have not been used in the region in appreciable amounts. The global distillation process can be understood using the same principles that explain distillations used to make liquor or purify chemicals in a laboratory. In these processes, a substance is vapourised at a relatively high temperature, and then the vapor travels to an area of lower temperature where it condenses. A similar phenomenon occurs on a global scale for certain chemicals. When these chemicals are released into the environment, some evaporates when ambient temperatures are warm, blows around on winds until temperatures are cooler, and then condensation occurs. Drops in temperature large enough to result in deposition can occur when chemicals are blown from warmer to cooler climates, or when seasons change. The net effect is atmospheric transport from low to high latitude and altitude. Since global distillation is a relatively slow process that relies on successive evaporation/condensation cycles, it is only effective for semi-volatile chemicals that break down very slowly in the environment, like DDT, polychlorinated biphenyls, and lindane.

Persistent organic pollutants (POPs) represent a group of anthropogenic organic chemicals of particular interest due to concern that they are resistant to degradation in the environment. Generally, POPs resist photolytic, biological or chemical degradation, in varying degrees, depending on their chemical structure. Since POPs possess low water solubility and high lipophilicity, they are subject to bioaccumulation in human and animal fatty tissues, and then biomagnify along food chains. Indeed, POPs are associated with chronic ecotoxicological effects [128–130].

Considering the major environmental and health aspects associated with POPs, considerable international efforts are being sought to control their worldwide distribution in the last decades. The Stockholm Convention on POPs classifies the following compounds as persistent: organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), with more compounds being proposed for listing. Under this treaty, parties and signatories should monitor these chemicals and identify their source, as well as develop a national inventory [131,132]. So far, a number of monitoring studies on atmospheric POPs on local, regional and global scale have been conducted [129,133]. However, tracing past use and atmospheric fate of these compounds are not an easy task [133,134].

POPs occur in typically very low atmospheric concentrations, such as ∼1 pg m−3 (1 ppq, parts per quatrillion) or even lower [133]. Considering such low ambient air concentration levels together with the large number and variety of POPs, there are considerable sampling and analytical challenges regarding their determination. In this way, it becomes highly necessary to sample air volumes that are large enough to overcome analytical limits of detection (LODs). Depending on the sampling site, it is advisable to sample air volumes of ∼50–100 m3 for vapour phase and ∼500–1000 m3 for particulate matter. POPs concentrations are variable both spatially and temporarily. Due to their low levels in air, they necessarily require elaborate sampling followed by high-performance, cost-effective analytical methods with skilled analysts. Real-time analysis of POPs is not yet feasible with existing instrument sensitivity [129,134].